1. Field of the Invention
The present invention relates to systems and methods for concealing the quality-degrading effects of packet loss in a speech or audio coder.
2. Background Art
In digital transmission of voice or audio signals through packet networks, the encoded voice/audio signals are typically divided into frames and then packaged into packets, where each packet may contain one or more frames of encoded voice/audio data. The packets are then transmitted over the packet networks. Sometimes some packets are lost, and sometimes some packets arrive too late to be useful, and therefore are deemed lost. Such packet loss will cause significant degradation of audio quality unless special techniques are used to conceal the effects of packet loss. There exist prior-art packet loss concealment methods for full-band predictive coders based on an extrapolation of the excitation signal, which is sometimes also referred to as the prediction residual signal. For example, see U.S. Pat. No. 5,615,298 to Chen, entitled “Excitation Signal Synthesis during Frame Erasure or Packet Loss.” However, issues arise when such techniques are applied to sub-band predictive coders such as the ITU-T Recommendation G.722 wideband speech coder due at least in part to the architecture of those coders. A sub-band predictive coder first splits an input signal into different frequency bands using an analysis filter bank and then applies predictive coding to each of the sub-band signals. At the decoder side, the decoded sub-band signals are recombined in a synthesis filter bank into a full-band output signal.